Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $96.47   10.202%   $106.3119   $106.31   $106.30   $106.30  
  Purchase #2 $155.31   12.745%   $175.1043   $175.10   $175.10   $175.10  
  Purchase #3 $151.70   12.712%   $170.9841   $170.98   $171.00   $171.00  
  Purchase #4 $240.38   9.226%   $262.5575   $262.56   $262.55   $262.60  
  Purchase #5 $73.99   9.492%   $81.0131   $81.01   $81.00   $81.00  
  Purchase #6 $58.39   13.778%   $66.435   $66.44   $66.45   $66.40  
  Purchase #7 $121.50   13.208%   $137.5477   $137.55   $137.55   $137.50  
  7 purchase totals = $897.74       $999.9536   $999.95   $999.95   $999.90